APXS_Meridiani3: The Alpha Particle X-ray Spectrometer (APXS) allows
determination of the chemical composition of rocks and soil.  Alpha
particles and x-rays are emitted by the Curium-244 radioisotope
sources and cause electron disploacements with the atoms in the
bombarded area, resulting in a cascade of fluorescent x-rays at unique
energies for each atom in the periodic table. The aperture for
measurement is 28 mm in diameter. Intensities (in counts per seconds)
and energies (in eV) of these x-rays are registered in an x-ray
detector to produce s-ray spectra. If comparing two spectra, their
relative intensities at a given energy are proportional to the
elemental concentrations. However, the proportionality factors can be
complex, and are determined by an extensive calibration of the
instrument using well-analyzed geochemical standards.  Shown here are
full energy spectra of x-rays(plotted in log scale)taken from Tamaruc,
a soil patch at Meridiani, and from the rock McKittrick after its
surface was grinded by the RAT. High concentrations of sulfur and
bromine in this rock are evident.